Bradyetes inermis

Bradyetes cf. inermis

(Figs 3–4)

Material. Twenty three Bradyetes cf. inermis females attributed herein to 3 morphological types were sorted from the samples (Table 1).

Description. Bradyetes cf. inermis morphotypes 1–3 share the general characters described for the species by Markhaseva and Schulz (2006: 143–146), e.g., the body segmentation and caudal rami structure; the rostrum, which is formed as a rudimentary blunt plate, the genital double-somite, which is barrel-like and usually wider anteriorly, and the general details of the armament of oral parts (Table 3).

Bradyetes cf. inermis morphotypes 1–3 differ in the combination of the following characters (Figs 3–4): morphotype 1 (Fig. 4), body length 2.60–3.00 mm, is characterized by 1) a sausage-like spermatheca that has nearly the same width proximally and distally, 2) a maxillule praecoxal arthrite with 11 setae: 8 long plus 1 short terminal setae (marked by a star in Fig. 4), 1 anterior and 1 posterior setae (this short terminal seta is absent in morphotypes 2 and 3), and 3) a P1 with a well-developed lateral lobe on the endopod and a plumose basal medial seta (this lobe is poorly developed or absent and the medial seta is nude in morphotypes 2 and 3). Morphotype 1 shares with morphotype 2 the maxillular epipodite which is equipped with 8 setae (6–7 setae are present in morphotype 3).

Morphotype 2 (Fig. 4), body length 2.50 mm, is characterized by a maxillule praecoxal arthrite with 9 setae: 8 long terminal setae plus 1 anterior seta, short terminal seta and posterior seta are absent. Morphotype 2 shares the setation of the maxillule epipodite with morphotype 1. Morphotype 2 shares with morphotype 3 a narrow-elongate spermathecae that is slightly widened in the distal part, the P1 that lacks the lateral lobe at the endopod, and a nude basal medial seta at P1.

Morphotype 3 (Figs. 3–4), body length 2.50–2.95 mm, is characterized by 1) a maxillule praecoxal arthrite with 10 setae: 8 long terminal, 1 anterior and 1 posterior setae; 2) a maxillule epipodite with 6–7 setae. Morphotype 3 is similar to morphotype 2 in lacking the P1 endopod lateral lobe and in having a nude basal medial seta and elongate spermathecae, which is slightly widened distally. The shape of the spermathecae varies slightly among the specimens of morphotype 3.

Remarks. The species Bradyetes inermis was established by Farran (1905) based on a single specimen from the North Atlantic (at about 53° N 12° W) collected from a depth of 358 m. The other taxonomic notes on B. inermis records are brief comments on the first finding of its male with incompletely detailed figures of both sexes in Grice (1972) and a recent record by Markhaseva & Schulz (2006) with an illustrated description of females.

Markhaseva & Schulz (2006), however, postponed a final decision on the specific status of their specimens and referred to them as Bradyetes cf. inermis, because of inconsistent and insufficiently detailed existing descriptions of B. inermis.

In 2016 it was clarified that the type specimen of B. inermis was most likely lost (Paolo Viscardi, National Museum of Ireland, Natural History, personal communication) and none of the newly obtained specimens were found in or close to the B. inermis type locality. Therefore, due to the incomplete species description (Farran 1905) and until possible specimens of this species are found in the type locality, it remains impossible to confirm or disprove that the available B. cf. inermis specimens belong to B. inermis sensu Farran.

All recently captured B. cf. inermis individuals were collected in deep waters (Table 1) and were regarded as belonging to 3 different morphotypes. Specimens identified as morphotypes 1 and 2 (Table 1, Figs. 4, 9) were found in the Atlantic Ocean only. Bradyetes inermis sensu Grice (1972), also found in the Atlantic, more probably belongs to morphotype 1 (e.g., similar shape of spemathecae and P1 endopod supplied with a lateral lobe).

Bradyetes cf. inermis morphotype 3 appears to be the most widely distributed morphotype, as it was recorded from the Atlantic, Southern and Pacific Oceans (Table 1, Figs. 3–4, 9). Morphotype 3 specimens from different geographical regions share the setation of maxillule and mandible and a similar P1 morphology. They demonstrate variability of the shape of the genital double somite and the spermathecae, but this variability among the Pacific specimens from one region (Kurile-Kamchatka Trench) is at least as high as between specimens from different oceans (Figs. 3–4).

In regard to the identity of Bradyetes cf. inermis specimens from the Atlantic and Southern Oceans with the individuals from the Pacific Ocean we rely only on their morphological comparisons as molecular data is currently impossible to obtain, because of a lack of specimens from the Atlantic and Southern oceans, which are suitably preserved for molecular analysis.

Species groups in Bradyetes . Classical morphological analysis shows that the genus Bradyetes is subdivided into two species groups.

Group I includes the species B. curvicornis, B. cf. inermis, B. pacificus and B. weddellanus. Females of this group share 1) a body size of 2.50–5.50 mm; 2) a genital double-somite that is longer than wide, of a barrel-like or close to barrel-like shape; 3) a narrow spermathecae, which is not much wider than the duct leading to the genital atrium, or sausage-like; 4) an antennule with ancestral segment I with 1 seta; 5) an antenna with a setal formula of 1-1,1-1,1,1,1,1,1(0) and 3 setae, and fused proximal exopod segments 1–2 and 3–4 (differs in B. pacificus); 6) a mandible basis with 1 seta, and an endopod segment 1 with 1 seta (or seta absent), and endopod segment 2 with less than 6 setae; 7) a maxillule coxal endite with 4 setae, proximal basal endite with 3 setae, distal basal endite with 4 setae, endopod with fewer than 15 setae, and an exopod with 11 setae; 8) a maxilla endopod with 7 or 8 setae; 9) a maxilliped coxa with an aesthetasc-like appendage, and 10) a nude posterior surface of segments of the P2–P4 endopods. Males are defined by one-segmented left P5 endopod (Table 3).

Group II includes the species B. matthei and the new species Bradyetes paramatthei sp. nov. The females of this group are defined by: 1) a body size of 1.19–2.30 mm; 2) a genital double-somite of globular shape; 3) a large spermathecae, round to oval-round with a narrow duct leading to the genital atrium; 4) an antennule ancestral segment I with 2? or 3 setae; 5) unclear antenna exopod fusions and uncertain setal formula interpretation 0(1)?0?1?1,1,1,1,1,1 and 3, with at least one seta lost from proximal exopod segments 1–4; 6) a mandible basis and endopod segment 1 with 2 setae each and endopod segment 2 with 9 or 9+1 setae; 7) a maxillule coxal endite with 5 setae, proximal basal endite with 4 setae, distal basal endite with 5 setae, endopod with 15–16 setae, and an exopod with 9–10 setae; 8) a maxilla endopod with 9 setae; 9) a maxilliped coxa without an aesthetasc-like appendage, but equipped with a conical tubercle; 9) posterior surface spinules that are present at least on some of the P2–P4 endopod segments. Males are defined by a two-segmented left endopod in P5.

Cladistic analysis. The parsimony analysis recovered two most parsimonious trees with 49 steps (consistency index = 0.898, retention index = 0.938). The 50% majority rule topology was identical with the strict consensus tree (Fig. 10A). The analysis confirms that Bradyetes falls into two clades: one comprising B. curvicornis, the three morphotypes of B. cf. inermis, B. pacificus, and B. weddellanus (Group I) and the other containing B. matthei and the new species B. paramatthei (Group II). The monophyly of Group I is very strongly supported (bootstrap value [BV] = 100%, Bremer index [BI] = 11), whereas Group II has a relatively weak support (BV = 88%, BI = 2). Both groups together form a well-supported clade (BV = 97%, BI = 3). Within Group I, B. pacificus is robustly resolved as sister to the remaining species. The three morphotypes of B. inermis form a weakly-supported monophyletic clade (BV = 61%, BI = 1), with morphotypes 2 and 3 being more closely related than morphotype 1.

The Bayesian analysis yielded a similar, but less resolved topology compared to the parsimony analysis (Fig. 10B). Groups I and II were recovered as monophyletic, with Group I being highly robust (posterior probability [PP] = 97%) and Group II only weakly supported (PP = 89%). The relationships within Group I are mostly unresolved, except for morphotypes 2 and 3 of B. inermis, which form a monophyletic group, albeit with a weak support (PP = 84%).